The disclosed invention relates to electronically controlled braking systems. Specifically, the present invention relates to a braking system wherein a brake command circuit cooperates with skid control circuitry to provide electrical control of a brake servo valve which meters the hydraulic pressure applied to appropriate brake cylinders.
The prior art includes electronically controlled braking systems wherein operator pedal actuated transducers and skid control circuitry cooperate to determine a braking pressure. However, a major disadvantage of such prior art systems is the fact that the skid control circuitry reduces the braking pressure solely as a function of the skid control circuitry output. That is, the reduction in brake pressure is an absolute amount determined by the skid control circuitry, irrespective of the brake pressure being commanded by the operator.
For example, in a subtractive braking system wherein the skid control circuitry functions to subtract from the operator brake command signal, an overdump condition can easily occur. This is particularly critical where less than full pressure is commanded by the operator and the skid control circuitry commands a pressure release having a value greater than the value of the commanded pressure.
Thus, it is readily apparent that prior art electronically controlled braking systems wherein antiskid pressure reduction is independent of actual brake pressure are inefficient, thereby resulting in slow brake pressure recovery and excessive braking distances.
The prior art further includes automatic braking systems wherein a desired rate of deceleration is preselected by the operator, and an electronic control circuit provides a brake signal which is indicative of the brake pressure required for the preselected rate of deceleration. Such prior art systems also include skid control circuitry, but these systems generally operate in a manner wherein the skid control circuit will control brake pressure if the skid control circuit calls for a lower braking pressure. With such systems, overdump conditions can also readily occur, resulting in braking system inefficiency. Further disadvantages of prior art automatic braking systems include the extensive use of mechanical and hydraulic controls for controlling brake pressure, and the resulting complexity of the necessary mechanical and hydraulic hardware.
It is, therefore, an object of the present invention to provide an electronically controlled braking system having skid control which is a function of the commanded brake pressure.
A further object of this invention is to provide an electronically controlled braking system wherein the amount of skid control brake pressure release is a function of the brake pressure commanded.
Still another object of the present invention is to provide a braking system wherein brake pressure is electronically controlled by an operator-actuated electrical circuit and a skid control circuit.
Another object of the present invention is to provide a braking system wherein skid control circuitry modifies an operator-commanded brake pressure signal as a function of the commanded brake pressure signal.
A further object of the present invention is to provide a selected deceleration braking system wherein electronic controls are utilized to control brake pressure.
Another object of this invention is to provide a selected deceleration braking system wherein a brake command signal is modified by a skid control circuit as a function of the brake command signal.